Lamella Mixer CHEM-E7160- FLUID FLOW IN PROCESS UNITS MOHAMMED REFAAT JUSRI HASSANEIN JAMA ALI

The context Introduction Modelling lamella mixer Relevant Equations Results Discussion/ Conclusion

Introduction Lamella mixing at microscale level better selectivity, yield, process safety computational fluid dynamics (CFD) can provide information about mixing efficiency and geometrical effects

Modelling lamella mixer 3 models where created using Google Sketch up and Autocad all 3 models consisted of variating shaped chambers(triangular, rectangular and slit-shape) and constant size of microchannels with cross secton of 20 micrometer and 10 micrometer height Two fluids with different of concentrations upper 100 mol/m^3 and lower 0 mol/m^3 enter the chambers through three and three small microchannels. Pressure differences of the front end and back end is driving force. Mixing of the the fluids will occur in the chamber

Lamella mixer with triangular chamber Chamber length 100µm and height 10 µm.

Lamella mixer with rectangular chamber Chamber length 100 µm and height 10 µm.

Lamella mixer with slit-shape chamber Chamber length 100 µm and height 10 µm (geometry is divided at half of the length).

Model description The 3 models in comsol analyze the fluid flow in steady-state condition, diffusion and dissolved substance which is examined through concentration profile Additionally, the effects of geometries , velocity, different mesh options and discretization methods on the concentration profile were examined After running the models the mixing chambers were divided into 4 different locations to obtain the concentration profiles

Equations The fluid flow in the channels and in the chambers can be solved with Navier-stokes equation(1) The concentration the dissolved matter can be solved with convection-diffusion equation(2) The micromixing that occurs in the chambers can be described with energy dissipation rate equation(3)

Results Velocity profiles It can be seen the change in the velocity magnitude across the slices in each geometry and higher velocity occurred in the triangular.

Concentration distribution At the entrance of the mixing chamber the concentration will gradually mix towards the end part of the chamber. The mixing is more rapid at the edges of the chamber compared to the middle part due to the slow velocity.

Diffusion Coefficient A slight change in the diffusion coefficient from 1E-10 m²/s to 1E-09 m²/s has a direct impact on the mixing efficiency. Effect of the diffusion Coefficient from 1E-10 m²/s to 1E-09 m²/s.

The concentration distribution across chamber 4 cut lines was inserted in the center of the chamber followed by plotting the concentration profiles. Effect on the concentration distribution by changing the diffusion coefficient from1E-10 m²/s to 1E-09 m²/s.

Discussion/ Conclusion The mixing was achieved by using laminar layered flow in micro level scale. The mixing chamber geometry was not critical in achieving effective mixing. The diffusion coefficient value and the velocity range inside the model are the key factors to obtain effective mixing. In order to enhance the mixing, longer mixing chamber is required, decrease flow velocity, and increase diffusion coefficient.

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